1. Field of the Invention
The present invention generally relates to atomic layer deposition (ALD) technology, particularly, to a method for depositing a silicon-containing film using two precursors by ALD.
2. Description of the Related Art
Conventionally, in the field of semiconductor manufacturing, a high-quality thin film is deposited on a substrate typically by chemical vapor deposition (CVD). Recently, in connection with development of super fine semiconductor devices, ALD technology, wherein a thin film is formed on a substrate by laminating atomic layers one by one, has been examined. In ALD, a gas-phase source gas is introduced to a chamber wherein a substrate is placed, and approximately one molecule in thickness is chemisorbed to a surface of the substrate. The gas-phase source gas is then purged from the chamber, and for example, an oxygen source for forming an oxide film or a nitrogen source gas for forming a nitride film is introduced, thereby causing reaction with the source gas chemisorbed on the surface of the substrate and forming a thin layer composed typically of less than one molecular layer in thickness. The reaction gas is then purged from the chamber, and the above steps are repeated to form a thin film having a desired thickness.
As described above, because ALD utilizes chemisorptions of a source gas on a surface of a substrate, ALD is characterized by excellent step coverage, and a good film can be formed at a temperature of 300 to 650° C. or a temperature lower than the foregoing. Thus, ALD is believed to be useful technology not only for forming gate insulation films, but also for forming dielectric films such as SiC films used as an etch stopper for an underlying layer having a complex shape or pattern or as copper diffusion blocking films.
However, because ALD deposits atomic layers one by one by repeating the steps described above, there is a problem of a low throughput of the film forming processes, and when forming a thick film, the steps must be repeated for a high number of times. Further, in ALD, some precursors are not easily chemisorbed on a surface of a substrate. For example, deposition of SiN film is challenging. In practice, the only organosilicon precursors feasible for SiN deposition are those containing no oxygen, and therefore, the prime candidates are silicon alkylamides, which are volatile enough to be used in practical applications, but thermal and also plasma-enhanced ALD of SiN from these precursors has not yet been successful.
In contrast, CVD, which has been used for forming similar films, is capable of efficiently forming a film in an extremely short amount of time by introducing both a gas-phase source gas and a reactant gas to a chamber. However, when a thin film is formed by plasma CVD on a semiconductor circuit having irregular surfaces, the step coverage is normally as low as about 70%. Further, as semiconductor devices become finer, an aspect ratio, which is a ratio of opening size to depth of the opening, becomes larger, and thus, the step coverage of films by CVD is expected to be even lower than today. Further, for example, when a SiN film is formed at least partially by CVD, material properties of the film tend to be changed in trenches.
In the present invention, one object, among others, is providing a method of forming a film in which a low throughput, which is a shortcoming of ALD, is improved.
Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion were known at the time the invention was made.